1. Field of the Invention
This invention relates to a submersible pump assembly wherein a plurality of pump stages as well as a discharge head and an inlet base are pressed under pressure into a casing, and the latter is then roll-formed to maintain the discharge head, the stages and the inlet base in assembled, aligned relationship.
2. Description of the Prior Art
Over the years, much effort has been expended toward optimization of pump performance. Desirably, pumps should utilize a minimum of motor horsepower while providing a maximum flow rate and discharge pressure. In addition, submersible pumps are faced with size restrictions due to the diameter of the well pipe. Moreover, access to such submersible pumps is often somewhat difficult and thus these pumps should operate reliably over extended periods without maintenance.
As is known, conventional submersible pumps are comprised of an inlet base, a stack of pumps stages above the base, and a discharge head on the upper end of the stack remote from the base. A casing surrounds the stages and is secured to the head and the base. A drive shaft, coupled to a motor armature, extends axially through the stack and is fixed to an impeller within each of the stages. Rotation of the drive shaft thus turns each impeller to force fluid radially outward toward an adjacent, stationary diffuser, and in turn the cooperating diffuser directs the fluid radially inwardly and upwardly toward the next pump stage.
In the past, certain submersible pumps have been provided with a thin, metallic casing having formed screw threads which are engageable with complemental threads on the discharge head and the base. During assembly, the stages are slipped into the casing and the head and base are then threaded into the casing until engaging respective ends of the staging stack. The diffusers of such pumps are thus held stationary by the axial force exerted on the staging stack by the head and base once the latter are tightened.
Unfortunately, in such prior art pumps, the axial force of the head and base against the staging is sometimes insufficient to preclude movement of the diffusers in a direction laterally of the staging stack. Moreover, such axial forces are occasionally unable to provide sufficient frictional forces to preclude rotation of the diffusers. As a result, efficiency of the pump is reduced substantially and the latter must then be removed from the well, often at great expense, for servicing.